Grey Leaf Spot is a fungal disease affecting fruits of the Tomato plant. It is found in crops cultivated all over the world, but particularly those in regions with warm climates. Peppers, Eggplants, and Corn are among other plants also susceptible to infection by Grey Leaf Spot.
Grey Leaf Spot is caused by the plant pathogens Stemphylium botryosum f.sp. lycopersici, Stemphylium lycopersici, Stemphylium floridanum, and Stemphylium solani. These spores flourish in warm environments, where there is alternation between wetness and dryness of the cultivation site. Once the condition has set on, it cannot be reversed.
The main harm that the disease causes to the Tomato plant is that it impedes the maturation of seedling foliage into mature stage plant foliage. Expanding brown, gray, yellow lesions on the leaves of the affected plant slowly dry and leave holes- or, in particularly severe cases, cause the whole leaf to fall off. The loss and destruction of leaves can result in sunburn to the fruits. This said, the disease does not directly attack the fruits. Below are some images of Tomato plants affected with Grey Leaf Spot:
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http://farm4.static.flickr.com/3633/3560099889_6dee69d930.jpg
Though there do exist some Grey Leaf Spot varieties of Tomato plants, there are also many ways of preventing the onset of the disease in susceptible species. For one thing, fungicides such as “Zero Multi-purpose Fungicide®,” “Bravo®,” or “Garden Fungicide Spray®” can be applied to the plants in very early stages of the disease. For another, irrigation systems really do matter in preventing the onset of Grey Leaf Spot. While overhead sprinkler systems aid the growth of the fungus, furrow or drip irrigation systems are a safer way to water crops but not endanger them. Furthermore, the fungus spores that cause the disease can survive throughout the seasons on Solanaceous weeds, which is why it is important to maintain a clear patch of soil for growing Tomatoes.
Septoria leaf, early leaf blight, and late blight are other fungal diseases that affect Tomato plants, and that are some times confused with Grey Leaf Sport. They are, however, separate diseases.
Sources Cited:
http://www.greenfingers.com.au/services/digging_deeper/tomatoes_want_to_grow/5.htm
http://www.spectrumbrandshomeandgarden.com/SolutionCenter/LawnTips/Grey+Leaf+Spot.htm
http://www.avrdc.org/pdf/tomato/gray_leaf_spot.pdf
http://www.extension.iastate.edu/CropNews/2009/0721Robertson.htm
